Technical Field
The present disclosure relates to the field of wireless communication, and particularly, to a power control method and user equipment in device to device (D2D) communication in a serving cell.
Description of the Related Art
The D2D communication is direct communication between devices, and such kind of communication could happen within network coverage and without network coverage.
FIG. 1 shows a situation in which D2D direct communication is performed within network coverage and D2D direct communication is performed without network coverage.
As shown in FIG. 1, user equipments 101 and 102 directly communicate within network coverage of an E-UTRAN node B (eNB) 100, while user equipments 103 and 104 directly communicate without network coverage of the eNB 100.
When D2D user equipments are in a Long Term Evolution (LTE) wide area network (WAN), they may be operated in LTE WAN and D2D communication simultaneously. That means, in some radio resources/subframes, D2D user equipments transmit/receive LTE WAN signals, but in other radio resources/subframes, D2D user equipments transmit/receive D2D signals. This also depends on which mode D2D user equipments are operated in. Currently there are two modes that a user equipment could be operated in: mode 1 in which an eNB (like base station) or a release-10 relay node schedules exact resources used by a user equipment to transmit direct data and direct control information; and mode 2 in which a user equipment on its own selects resources from resource pools to transmit direct data and direct control information.
In mode 1, the resources for D2D transmission are allocated or fully controlled by the eNB, but in mode 2, the user equipment itself selects the resources for D2D transmission. Generally, in mode 1, D2D user equipments (for example in RRC_CONNECTED) could receive dedicated RRC signaling from the eNB, but in mode 2, D2D user equipments (for example in RRC_IDLE) can only receive common RRC signaling, for example, a system information block (SIB). In this document, the focus is mainly user equipments in mode 1.
If D2D resources and LTE WAN resources are multiplexed in the same subframe, there are problems of in-band emission and inter-carrier interference. The first problem means that a D2D signal may cause power leakage to neighbor LTE WAN signals in the frequency domain in the same subframe. The second problem somehow has a meaning similar to the first problem but it may be caused by other reasons, for example, whether the timing of signals are aligned. If a D2D signal uses an extended cyclic prefix (CP) but an LTE WAN signal uses a normal CP (NCP), which means the timing of two types of signals are not aligned, it may lead to inter-carrier interference.